The present invention relates to a novel room temperature curable organopolysiloxane composition storable as one package with extended storability in a tightly sealed vessel and with improved curability in the open air atmosphere.
In the prior art, various types of room temperature curable organopolysiloxane compositions are known which are stable in a tightly sealed vessel and curable in the open air atmosphere even at room temperature by reaction with atmospheric moisture to be converted into a rubber-like elastomer. These organopolysiloxane compositions fall into two classes, i.e., (1) two-package type where the contents of two separate packages are mixed just prior to use and (2) one-package type where the compositions are mixed and stored in one package. The compositions of the latter type are prevailing in general owing to convenience in use as a sealing material, caulking material, adhesive material and the like.
The one-package type room temperature organopolysiloxane compositions are also classified into several groups according to the mechanisms of their crosslink formation by condensation reaction evolving carboxylic acids, amines, oximes or alcohols as the condensation products. Among the four groups of the compositions, the first three have the disadvantages that the carboxylic acids, amines or oximes liberated by the condensation reaction in the crosslink formation in air are toxic or corrosive with offensive odors so that powerful ventilation is indispensable in the use of the compositions as well as the necessity of primer treatment prior to use in order to prevent rusting of a metal substrate.
On the other hand, the compositions curable by the mechanism of dealcoholation condensation are free from the problems due to the formation of toxic or corrosive gases. However, they suffer from the problems of their poor storability as well as rather slow curing velocity at room temperature, especially in the depths farther from the surface, and the poor mechanical properties or brittleness of the cured products. In addition, the alkoxy titanate compounds as the curing accelerator necessitated in these compositions remain in the cured products and cause coloration or lowering of thermal stability to the products.
Similarly, the metal salts of organic acids used at the curing catalyst in the compositions curable by the mechanisms of liberating carboxylic acids, oximes or alcohols also remain in the cured products, sometimes resulting in offering some problems due to their toxicity.
Recently, room temperature curable organopolysiloxane compositions of a novel type have been disclosed in U.S. Pat. No. 3,819,563 according to which the compositions are cured by the atmospheric moisture liberating a ketone. These compositions are free from the problems with respect to adhesiveness or corrosiveness, but still not satisfactory due to unpleasant odors emitted in the course of curing.